Burner control unit

ABSTRACT

Control apparatus for a burner installation including two shutoff valves in a line for supplying fuel to the burner, which comprises means for testing the effective closure of each of the valves by applying a source of suction pressure to the volume in the fuel line between the valves and checking by pressure sensing means that the reduction of the pressure in the volume is consistent with the two valves being closed.

United States Patent Inventors Roger A. Hancock;

David J. Moppett, both of Solihull, England Appl. N0v 805,631 FiledPatented Assignee Mar. 10, 1969 June 8, 1971 The Gas Council London,England Priority Mar. 12, 1968 Great Britain BURNER CONTROL UNIT 26Claims, 5 Drawing Figs.

US. Cl

References Cited UNITED STATES PATENTS 2,707,390 5/1955 Beretish 73/463,358,732 12/1967 Stuart 431/22 FOREIGN PATENTS 603,423 8/1960 Canada431/16 Primary Examiner-Carroll B. Dority, Jr. Attorney-Kemon, Palmerand Estabrook ABSTRACT: Control apparatus for a burner installation including two shutoff valves in a line for supplying fuel to the burner,which comprises means for testing the effective closure of each of thevalves by applying a source of suction pressure to the volume in thefuel line between the valves and checking by pressure sensing means thatthe reduction of the pressure in the volume is consistent with the twovalves being closed.

1 0 15 13 I X I X 1 PATENTEU JUN 8:911 3,583,842

sum 1 OF 4 PATENTEU-JUN 81971 3.583842 SHEET $.UF 4

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c3 W H M Z5 87 L/VE E 1 1 2 NEUTRAL 7724 74 g Qw -29 P83 K A ,+F-q 3PRESSURE EN I we s [4 T82 84 swag ecu B W187 0 M W Z5 LIVE NEUTRAL Q I vfz wm/b inf "I v 04 3,, 9 A am m BURNER CONTROL UNIT This inventionrelates to apparatus, generally known as a burner control unit, forautomatically controlling a burner installation.

The present invention consists in apparatus for automaticallycontrolling a burner installation having fuel shutoff means in a linefor supplying fuel to the burner comprising means for testing theeffectivenessof the closure of the fuel shutoff means, means forinitiating each of the steps necessary for starting up and/or shuttingdown the burner in time ordered sequence and including the actuation ofthe testing means prior to the opening of the fuel shutoff means and/orafter its closure.

The present invention provides combined apparatus for controlling theburner control and testing the fuel valves.

The fuel shutoff means may comprise two ,fuel shutoff valves in seriesin the line for supplying fuel to the burner and the means for testingthe effectiveness of the closure of the fuel shutoff means comprisesmeans for testing the effective closure of each of the fuel valves.

The fuel valves may each be in the form ofa slide, gate or, sluicevalve, or they may be a disc-on-seat type of valve, a rotary cock typeor any other type of valve. The fuel valves may be combined in a singleunit in which two sets ofsealing means are provided between the movablemember of the valve and the seat, the arrangement being such that whenclosed the two sets of sealing means define between them a volume whichis utilized by the apparatus according to the invention as will bedescribed hereinafter.

This invention relates to apparatus, generally known .as a burnercontrol unit, for automatically controlling a burner installation.

The present invention consists in apparatus for automaticallycontrolling a burner installation having fuel shutoff means in a linefor supplying fuel to the burner comprising means for testing theeffectiveness of the closure of the fuel shutoff means, means forinitiating each of the steps necessary for starting up and/or shuttingdown the burner in time ordered sequence and including the actuation ofthe testing means prior to the opening of the fuel shutoff means and/orafter its closure.

The present invention provides combined apparatus for controlling theburner control and testing the fuel'valves.

The fuel shutoff means may comprise No fuel shutoff valves in series inthe line for supplying fuel to the burner and the means for testing theeffectiveness of the closure of the fuel shutoff means comprises meansfor testing the effective closure of each of the fuel valves.

The fuel valves may each be in the form ofa slide, gate or, sluicevalve, or they may be a disc-on-seat type of valve, a rotary cock typeor any other type of valve. The fuel valves may be combined in a singleunit in which two sets of sealing means are provided between the movablemember of the valve and the seat, the arrangement being such that whenclosed the two sets of sealing means define between them a volume whichis utilized by the apparatus according to the invention as will bedescribed hereinafter.

Embodiments of the inventionwill now be described, by way of exampleonly, with reference to the accompanying drawings in which:

FIG. 1 is a diagram of part of a burner installation comprising testingapparatus included in the apparatus accordingto the invention forautomatically controlling the burner installation;

FIG. 2 is a schematic circuit diagram of one form of apparatus forautomatically controlling a burner installation according to theinvention;

FIG. 2a is a continuation of the diagram ofFlG. 2;

FIG. 3 is a schematic circuit diagram ofa modified form of the apparatushaving a circuit diagram according to FIGS. 2 and 2a; and

FIG. 3a is a continuation of the diagram of FIG. 3.

In FIG. 1, a fuel supply line 10 to a burner 11 is controlled by twofuel valves 12 and 13 in series. Air is supplied to the burner 11 underpressure through line 14. For safety it is necessary to proveperiodically that when the fuel valves 12 and 13 are in the shutoffposition, they are both effectively closed. This is done by subjectingthe volume 15 between the fuel valves 12 and 13 to suction pressure andconfirming that the resulting pressure conditions in the volume areconsistent with the fuel valves being closed.

Testing apparatus for this purpose added to the basic burnerinstallation so far described is included in FIG. 1. The suction side ofan ejector 17 is connected through a stop valve 18 and a restrictingorifice 19 to the volume 15. The main flow of air for operating theejector 17 is in this example, provided from the air supply line 14through a branch pipe 20 including a stop valve 21. The stop valve 21 isnot essential to the valve testing procedure but its presence enablesthe ejector 17 to be shut off when not required and so removes a sourceof noise which could be objectionable.

A pressure sensitive switch 6 whose contacts are closed except when itis subjected to a predetermined subatmospheric pressure is alsoconnectedto the volume 15. The design of some burners to which this testingapparatus might be applied is such that quite large subatmosphericpressures would be created in the fuel supply line 10. Such pressureswill occur not only when the burner is operative but also under testconditions while the fuel valves 12 and 13 are closed but air is flowingto the burner through air supply line 14 to operate the ejector 17. Toprevent the testing apparatus from indicating a safe condition when asuction leak through valve 13 exists, the predetermined subatmosphericpressure at which the pressure sensitive switch 6 is actuated must begreater than any subatmospheric pressure occurring in the fuel supplyline 10 downstream of valve 13. This requirement should be met eventhough suction pressure for the testing apparatus is not derived fromthe air supply line 14 since'the test procedure will usually be carriedout while the burner is being purged with air. This testing apparatushas the necessary provisions for carrying out two methods of confirmingthat the valves 12 and 13 are effectively closed.

ln the first'method ofconfirmation the volume 15 starts substantially atatmospheric pressure. The stop valves 18 and 21 are opened and theejector applies suction to the volume 15. The size of the orifice 19 issuch that a significant time interval elapses between the opening of thestop valve 21 and the opening of the pressure sensitive switch 6 at thepredetermined subatmospheric pressure. A check is made after apredetermined time interval that the pressure sensitive switch 0 hasopened.

If the second method of confirmation is also to start from the conditionin which the volume 15 is substantially at atmospheric pressure, thestop valves 18 and 21 are opened and the pressure in the volume 15reduced just below that at which the pressure sensitive switch 6 opens.The stop valve 18 is then automatically or manually closed and a checkmade after a predetermined time interval that the pressure sensitiveswitch 6 has not closed again and therefore that the pressure in thevolume 15 has not risen above the predetermined pressure.

If only the second method of confirmation is to be employed the orifice19 need not be provided. The provision of both stop valve 18 and orifice19, however, enables the two methods of confirmation to be combined.lmmediately after the opening of the pressure sensitive switch 6 at theend of the first method of confirmation the stop valve 18 is closed sothat the pressure in the volume 15 is only slightly less than thatnecessary to open .the pressure sensitive switch 6. A check is then madeafter a predetermined time interval, in accordance with the secondmethod of confirmation, that the pressure sensitive switch 6 has notclosed again and therefore that the pressure in the volume 15 has notrisen above the predetermined pressure.

The time intervals in the first. second and combined methods ofconfirmation may be checked by personal observation but this ispreferably done automatically by means which includes a timing deviceand which is used in the absence of correct conditions, to operate analarm and prevent the initiation of. or stop, a burner control run.

From the start at time T of a burner ignition sequence the first periodT is usually one in which air alone is allowed to flow to the burner.This is known as the prepurge period. In the installation of FIG. 1 thisair flows through line 14 and as this flow enables the ejector 17 to beenergized while the fuel valves 12 and 13 are closed, the prepurgeperiod T provides a convenient occasion for carrying out the testingprocedure.

The circuit diagram of FIG. 2 is for apparatus for automaticallycontrolling a burner installation including pilot and main burners, twosafety shutoff fuel valves in series being provided in the fuel supplyline to each burner.

The apparatus according to the invention comprises combined burnercontrol and fuel valve testing apparatus. For simplicity FIGS. 2 and 2ashow the circuit of the valve testing apparatus for the main valve only.The equivalent circuit for the pilot valve is a repetition of thediagram of FIG. 2a and the addition of two further pairs of contacts inthe remainder of the circuit shown in FIG. 2 as will be described later.

Reference numerals 22 and 23 indicate the live and neutral lines throughwhich electric power is supplied to the various components of thecombined apparatus.

A relay L/ll is connected to the lines 22, 23 by a start switch S and aninterlock circuit 85 through which there must be electrical continuitybefore the start switch S can operate the relay L/ll. Details of theinterlock circuit will be described later. The relay L/11 has a total ofeleven pairs of contacts of which seven L2, L3, L6, L8, L9, L and L11are normally open and four L1, L4, L5, and L7, are normally closed.

Timing of the burner control and valve testing sequence is by a camtimer having a synchronous motor SM which drives a set of cams actuatingpairs of contacts C1 to C4, C6 to C10 and C12 to C16 defining periods inthe sequence. The conventional designations for the time intervals inthe burner control period, which are used in this specification and areindicated on the drawing, together with typical durations for thepresent apparatus are as follows:

At the end of T the cam timer is back at the T position. T the air setdown period is a period for adjusting the air flow from the maximum flowused during the prepurge period to a reduced flow for ignition. In thepresent example the period T is not used but it may readily be providedif required. It has been introduced so that the designations of the timeintervals are consistent with those which would be used in apparatusrequiring a setdown period.

Testing the fuel safety shutoff valves is effected during the prepurgeperiod T and the post purge period T For testing purposes these periodsare subdivided as follows:

Period Description Approximate Duration TH Period for reducing pressurein the 2 seconds volume defined between the two shut-off valves inseries Tm Period for testing that the prel/2 second determined pressurehas been reached Tm Waiting period at reduced pressure 20 seconds THPeriod for testing that the prel/2 second determined pressure in thevolume has been maintained during T T 5 The remainder of the pre-purgeperiod Tm Post-purge period for reducing pressure 2 seconds in thevolume TH: Postpurge period for testing that the H2 secondpre-determined pressure has been reached T Post-purge waiting period atreduced 20 seconds pressure TM Postpurge period for testing that the 1/2second pre-determined pressure in the volume has been maintained duringTRIP T The remainder of the post-purge period The individual pairs ofcontacts of the cam timer are closed as follows:

These periods of closure are indicated in the drawing against theindividual contacts.

The circuit connecting the motor SM to the supply includes a line 25 inseries with two branches 28, 29 in parallel. Branch 28 comprises relaycontacts L1 and cam timer contacts C1 in series, and in branch 29 relaycontacts L2 and cam timer contacts C2 are connected in series.

The stop valves 18 and 21 of FIG. 1, for the purposes of the presentapparatus, are solenoid valves which are normally closed but are openedby energizing the solenoid means W. The solenoid means W is connected tothe supply by a line in series with two branches 81 and 82 in parallel.Branch 81 includes stop valve contacts C of the cam timer and normallyopen, relay contacts L3, in series. Branch 82 includes stop valvecontacts C7 of the cam timer and normally closed relay contacts L5 inseries.

A valve test alarm relay K/3 is connected to the supply through apressure sensitive switch 6, of which only the contacts 6 are shown inthe FIGS. 2a and 3a, the contacts 6 being connected in series withparallel branches 83, 84. Branch 83 includes normally open relaycontacts L9 and alarm contacts C4 of the cam timer in series. Branch 84includes further alarm contacts C6 of the cam timer and normally closedrelay contacts L4 connected in series.

The relay K/3 has three pairs of contacts K1, K2 which are normally openand isolating contacts R 3 which are normally closed. Contacts Kl whenclosed connect valve test alarm N to the electric supply. Contacts K2are hold-on contacts and are connected in series with contacts Z1 of apushbutton reset switch having two pairs of normally closed contacts 21and 22. When the relay K/3 has been actuated through contacts C4 or C6and the pressure sensitive switch 6, it is maintained through thehold-on contacts K2 and reset switch contacts 21 until the reset switchis actuated manually to open the contacts Z1. Normally closed relaycontacts K3 and normally closed reset switch contacts Z2 are connectedin series in the interlock circuit 85. The reset contacts 22 areprovided to prevent the dangerous practice of forcibly retaining thereset button in the reset position, by wedging for example.

A flame detector F/2 of suitable known type has a normally open pair ofcontacts F1 and a pair of normally closed contacts F2. A flame alarmrelay J/3 is connected to the supply through normally open relaycontacts L in series with parallel branches 86, 87. Branch 86 includesnormally open contacts F1 and flame detector contacts C of the camtimer, connected in series. Branch 87 includes normally closed contactsT 2 and flame detector contacts C16 of the cam timer. As the contacts F1and'FZ are respectively normally open and normally closed, the flamealarm relay will be actuated if the contacts F1 are closed when contactsC15 of the cam timer are closed or the contacts F2 have not opened whenthe contacts C16 are closed. The contacts C15 and C16 are thereforetimed to close at periods when there should be no flame or flamerespectively. The relay .l/3 has two normally open pairs of contacts J1and J2 and one normally closed pair of contacts J3. Contacts J1 whenclosed connect a flame alarm 88 to the electric supply. Contacts J2 arehold-on contacts and are connected in series with contacts R1 of apushbutton reset switch having two pairs of normally closed contacts R1and R2. When the flame alarm relay J/3 has been actuated throughcontacts C15 and F1 or C16 and F2 it is maintained through the hold-oncontacts J2 and reset switch contacts R1 until the reset switch isactuated manually to open the contacts RI. Normally closed contacts J3and reset contacts R2 are connected in series in the interlock circuit85. The contacts R2 are provided for the same reason as the contacts Z2to prevent abuse of the reset button.

An electric motor V driving the fan for the forced air supply to theburner is connected to the electric supply by a line 89 in series withtwo parallel branches 90 and 91. The branch 90 includes normally openrelay contacts L6 and fan contacts C8 of the cam timer, connected inseries. The branch 91 includes fan contacts C9 of the cam timer andnormally closed relay contacts L7 connected in series. The air supplyline is provided with an air flow or air pressure switch A which isclosed when the air flow or pressure is above a predetermined value. Theair pressure switch A is connected in series in the interlock circuit85. Contacts C10 of the cam timer are connected in parallel with theseries connected air pressure switch A and hold-on contacts L8.

The interlock circuit 85 in series between the start switch S and therelay L/11 comprises, all connected in series, the air pressure switchA, reset contacts R2 and Z2'relay contacts J3 and K3 and hold-oncontacts L8. As the air pressure switch A and the hold-on contacts L8are open at the start condition T they are short circuited at that timeby the contacts C10 ofthc cam timer. For a successful start therefore onclosing start switch S all the contacts R2, J3, Z2, and K3 must beclosed before the relay L/11 can be energized. After period T all thesecontacts and additionally air pressure switch A and hold-on contacts L8must remain closed.

Contacts equivalent to contacts K3 and 22 in the pilot burner testapparatus would in practice also be provided. These would be connectedin series in the interlock circuit 85 at point X and would also have tobe in the closed position at the start and to remain closed thereafterin a successful start, run and shut-down sequence.

Relay contacts L11 when closed makes the power supply available tocircuits for electrical ignition apparatus 1, the solenoid means P forthe pilot fuel shutoff valves and solenoid means M for the main fuelshutoff valves. Cam timer contacts C12 in series with the ignitionapparatus 1, C13 in series with solenoid means P and C14 in series withsolenoid means M control the application of the power supply to thesecomponents at the relevant times.

The full sequence of a successful burner control run is as follows:

The start switch S is closed manually and as cam timer contacts C10 areclosed during T provided that contacts R2, J3, Z2 and K3 are all closedrelay L/11 is energized. Relay contacts L6 close and as contacts C8 areclosed during T the fan V starts for the prepurge. Relay contacts L10also close and as contacts C15 are closed during T and T the flamedetector contacts Fl must not close, that is there must be no flamesimulation, or the flame alarm relay J/3 will be energized. Relaycontacts L2 close starting the cam timer motor SM as contacts C2 areclosed during T At the end of period T, contacts C10 open but relay L/llis maintained through pressure switch A and contacts L8. Since contactsL3 were closed on actuation of the relay L/11, when contacts C3 close atthe beginning of period T the solenoid means W is energized to open thestop valves and apply suction pressure to the volume between the twofuel shut-off valves. Contacts C3 remain closed for period T defining afirst predetermined time interval for the application of suctionpressure to the volume. At the end of T contacts C3 reopen causing thestop valves to close, isolating the volume which by the end of period Tshould be at a subatmospheric pressure sufficient to actuate thepressure sensitive switch 6 and open its contacts.

Relay contacts L9 are closed and for a short period T contacts C4 closeand provided that the pressure sensitive switch 6 has opened indicatingthat the predetermined suction pressure in the volume has been reached,the relay K/3 will not operate. No change of contacts occurs during Twhich constitutes a second predetermined time interval for proving thatthe fuel valves are maintaining the suction pressure in the volumebetween them. For a short period T the contacts C4 again close andprovided that the pressure sensitive switch 6 is still held open therelay K/3 will again not operate. Alternatively the cam timer could bemodified to close contacts C4 for the whole of the periods T T and T Atthe beginning of period T cam timer contacts C12 close to energize theelectrical spark ignition apparatus I. Cam timer contacts C13 also closeto energize solenoid means P and open the fuel shutoff valves for thepilot burner. The pilot burner lights and at the beginning of T the camtimer contacts C16 close. Provided that there is a flame at the pilotburner the flame detector contacts F2 will be open and the flame alarmrelay 1/3 will not be actuated.

At the beginning of period T cam timer contacts C close and the solenoidmeans M is energized to open the fuel shutoff valves for the mainburner. The pilot burner lights the main burner. At the end of period Tthe contacts C open, the fuel valves for the pilot burner close and thepilot flame goes out. The main flame is proved during period T At theend of period T contacts C open and the cam timer motor SM stops.

The main run period T, of indefinite length follows. During that periodcontact C16 remain closed so that the flame detector contacts 1 2 are incircuit with the relay 1/3 but provided they remain open the flame alarmrelay J/3 will not be actuated.

When the burner is to be shut down, the switch S is opened manually.This deenergizes the relay L/1l which opens contacts L11 thusdeenergizing solenoid means M and closing the main fuel shutoff valves:it also allows relay contacts L1, L4, L5 and L7 to close. Cam timercontacts C remained closed while the cam timer was at rest during periodT, and closure of contacts L1 restarts the cam timer motor SM. Thismarks the beginning of the postpurge period T The fan V energizedthrough branch while the relay L/11 was energized is kept runningthrough branch 91 by the reclosing of the contacts L7. Cam timercontacts C and C are both closed during period T, and contacts C remainclosed during period T Closure of relay contacts [4 and I5 bring camtimer contacts C and C, into circuit with the pressure test alarm relayK/3 and stop valve solenoid means W respectively. A test sequencesimilar to that performed during periods T to T is carried out duringperiods T to T, under the control of the cam timer contacts C6 and C7.At the end of period T cam timer contacts Cl open and the cam timerstops in the T position. Similarly cam timer contacts C open and the fandriving motor V stops.

The above described successful sequence may fail upon any one of severalcontingencies.

On closing the start switch S if either of the reset contacts R2 and 22are open or there is already a flame indication or valve test alarmcondition so that contacts 13 or R3 are open, the relay L/ll will notclose and the sequence will not begin.

After relay Llll has operated, if the contacts F1 are closed at T orduring T showing flame when there should be none, relay J/3 is operated,contacts J1 close to give the alarm, contacts J2 maintain the relay 1/3in the operated condition and contacts 33 open breaking the circuit ofrelay L/ll which reopens.

Again, after relay L/ll has operated, if, from period T onwards, the fanfails, the pressure switch A opens and relay L/ll reopens.

If relay L/ll reopens, contacts [I close and the cum timer motor SMcontinues to run through the full sequence back to the T position whereit stops due to the opening of contacts C]. A fuel valve test will bemade during periods T to T because contacts t4 and K5 are closed.Similarly the fan motor V will be energized through contacts t7 untilthe cam timer reaches the T position.

If at T or T the contacts of pressure switch 6 are closed relay K/3 isoperated. lts contacts K1 operate the valve test alarm N, contacts K2maintain the relay K/3 and contacts K3 open so that relay L/ll reopens.The cam timer runs on as described in the previous paragraph but thesecond series of tests will not be indicated as the relay K/3 hasalready operated.

If during periods T to T there is no flame or the flame goes out theflame detector contacts F2 will close the relay 1/3 will be operatedwith the results previously described for a flame indication at T orduring T,.

If during periods T or T the pressure switch 6 is closed, valve testalarm relay K/3 is operated as for the prepurge test at T or T and anyattempt to restart the burner will be abortive until relay K/3 has beenreset manually by use ofthe reset button to open contacts 21.

The method of retaining the alarm condition on relays K/3 and J/3 relieson electrically maintained relays. This can be undesirable since removalof the power either accidentally or deliberately from the control unitcould cancel the alarm before corrective action has been taken. Thisdefect can be over come by the use ofa mechanically-latching relay forthis duty. This would require some form of mechanical or electricalreset to unlatch the relay. However, the reset contacts R2 and resetcontacts 22 should still be manually operable.

The symbols used to refer to the main components of the apparatus areconsistent with Boolean terminology in which the bar operator representsNOT, for example A represents NOT A.

The conditions under which the individual functions controlled by theapparatus will be performed can be expressed in the form of algebraicequations in which the elements are connected by symbols namely theaddition symbol representing OR and the multiplication symbol xsimplified to a dot representing AND. The symbols used for the inputsand outputs of the apparatus are:

INPUTS A Air supply interlock indicating air 0 Pressure switchindicating negative pressure S Start device in on' or start position RFlame alarm reset device in reset position Z Valve test reset device inreset position F Flame detector indicating flame OUTPUTS J Flame alarmenergized K Test alarm energized M Main fuel valve energized P= Pilotfuel valve energized l= Ignition energized V Fan energized SM Cam timeroperating ln Boolean terminology the apparatus illustrated in thediagram satisfies the following equations.

The above equations do not include the term T since it is not shown onthe FIGURE accompanying this specification. However, if it is desirableto include a period T the term T, must be appropriately inserted intoequations i, v and vi.

FIGS. 3 and 3a show a schematic circuit diagram of a modified form ofthe apparatus having the circuit diagram of FIGS. 2 and 2a. Themodifications which are apparent in interlock circuit and in valve testalarm relay K/3 circuit, ensure that pressure sensitive switches A and Oare in their appropriate states before the start-up cycle can commence.

A relay B/l is connected in series with the pressure sensitive switch 6across the supply and in parallel with branch circuits 83, 84 and therelay K/3. Relay B/l has one set of contacts B1.

lnterlock circuit 85 is modified in that it is provided with two, twobranch parallel circuits in one branch of one ofwhich are cam timercontacts C10 while in the other branch are normally open contacts A ofthe air pressure switch. In one branch of the other parallel circuit arehold-on contacts L8 while in the other branch contacts B1 of relay B/lare connected in series with a further set of contacts A of the airpressure switch which are normally closed. These two parallel circuitsare connected in series with start switch S and relay L/ll together withthe remaining interlock circuit components, reset contacts R2, 22, relaycontacts 33 and K3, across the supply.

In operation at time T the contacts of the air pressure switch should bein their appropriate normal states, that is, contacts A should be openand contacts A closed. As pressure sensitive switch contacts 6 should beclosed at T relay B/l should be energized closing normally open contactsB1. Since cam timer contacts C10 are closed at T manual closing of startswitch S should energize relay L/ll provided no alarm relays have beenenergized.

At the end of period T contacts C10 open, but as the air pressure shouldbe at the predetermined value, relay L/ll is maintained through theclosure of normally open contacts A and hold-on contacts L8.

If contacts O are open at time T relay 8/1 is not energized and contactsB1 are open so that operation of start switch S does not energize relayL/ll. Similarly if normally closed air pressure switch contacts A areopen, relay L/ll cannot be energized.

To provide additional protection against false energization of one ormore of the ignition apparatus I and the solenoid means P and M of thefuel shutoff valves, a modification of the circuits shown in FIGS. 2 and3 could be made.

The modification comprises the provision of an extra pair of normallyclosed contacts on each of the valve test alarm relay K/3 and flamealarm relay 1/3. These contacts jand K are connected in series withcontacts L11 of relay L/ll as shown in dotted outline on H05. 2 and 3.If either alarm relay is energized the associated contacts I, K, areopened and no energization of I, P or M can take place.

We claim:

1. An automatically controlled burner installation comprising a burner,a fuel supply line to said burner, two fuel shutoff valves connected inseries in said line and defining between them an enclosure, means fortesting the effectiveness of closure of said shutoff valves, and meansfor automatically controlling the operation of said burner, said meansincluding a timing device, said timing device enabling said controlmeans to control the operation of said burner in timed order, saidcontrol means causing the actuation of said testing means in a period inwhich the valves are closed, said testing means including a pressuresensor which can be put in fluid communication with said enclosure, anda source of suction applicable to said enclosure, and means forapplying, during a test, said source of suction to said enclosure toreduce the pressure in said enclosure, a check being made after apredetermined time by said pressure sensor that the pressure conditionsin said enclosure prove that said shutoff valves are closed.

2. A burner installation according to claim 1 wherein the pressuresensor comprises a pressure sensitive switch actuated when subjected toa predetermined reduced pressure.

3. A burner installation according to claim 2 and which includes anelectrically operated valve test alarm, said timing device of saidcontrol means having alarm contacts operative in an alarm actuatingcircuit, the pressure sensitive switch also being included in the alarmactuating circuit the arrangement of which is such that the alarm willbe operated upon the actuation of the alarm contacts of the timingdevice unless the pressure sensitive switch is in the actuatedcondition.

4. A burner installation according to claim 3 wherein said means forapplying said source of suction to said enclosure comprises arestricting orifice and a stop valve between said enclosure and saidsource of suction and wherein means for operating the stop valve iselectrically operated and the stop valve operating means includes in itscircuit stop valve contacts of the timing device, which are so actuatedthat the stop valve is open for a first predetermined time intervaltimed by the timing device to open the source of suction to theenclosure and shut for a second predetermined time interval timed by thetiming device, the alarm contacts of the timing device being actuated atthe ends of both the first and second predetermined time intervals.

5. A burner installation according to claim 3 comprising isolatingcontacts operated on actuation of the alarm and included in an interlockcircuit of the installation in a manner such as to prohibit, under alarmconditions, the initiation or continuation ofa burner control run.

6. A burner installation according to claim 3 wherein the alarmactuating circuit includes a relay and wherein means are provided formaintaining the alarm until cancelled by operation of reset means.

7. A burner installation according to claim 6 and comprising isolatingcontacts included in an interlock circuit of the apparatus in which therelay operates said isolating contacts in the interlock circuit.

8. A burner installation according to claim 6 in which the relayoperates a pair of contacts connected in series in a circuit with thealarm.

9. A burner installation according to claim 6 and having an interlockcircuit wherein the reset means operates isolating contacts included inthe interlock circuit in series and operating in a manner such as toprohibit the initiation or continuation ofa burner control run unlessthe reset means is in the inoperative condition.

10. A burner installation according to claim 3 wherein means areprovided for ensuring the return of the timing device to its startingposition whenever the electrically operated alarm is actuated.

11. A burner installation according to claim 3 in which actuation of thetesting means takes place prior to the opening of the fuel shutoffvalves and also after the closure of said valves wherein there areprovided circuits alternative to those operative for the testingsequence prior to opening the fuel valves, the timing device having apair of contacts in each of the circuits and actuable to determine aperiod during which each of the alternative circuits is operative.

12. A burner installation according to claim 11 wherein there isprovided in each of the alternative circuits a pair of isolatingcontacts operable so as to isolate one of the alternative circuits whenthe other is to be operative.

13. A burner installation according to claim 11 and including a stopvalve operated by electrical means including a circuit having stop valvecontacts of the timing device wherein there is connected across thecontacts of the timing device in the stop valve operating circuit afurther set of contacts of the timing device operating for the testingof fuel shutoff valves after the closure of said shutoff valves, saidfurther set of contacts being so actuated that the stop valve is openfor a first predetermined time interval timed by the timing device toopen the source of suction pressure to the volume and shut for a secondpredetermined time interval by the timing device, said alarm contacts ofsaid timing device being actuated at the ends of both the first andsecond predetermined time intervals.

14. A burner installation according to claim 13 wherein there isprovided a set of isolating contacts in series with each of the pairs ofcontacts of the timing device, one set of isolating contacts beingclosed when the other set are open.

15. A burner installation according to claim 12 and having an interlockcircuit including a relay, and alternative valve test alarm actuatingcircuits comprising isolating contacts wherein the isolating contactsare operated by said interlock circuit relay.

16. A burner installation according to claim 14 having an interlockcircuit including a relay and a stop valve operated by one of two setsof stop valve contacts in parallel, each set being connected in serieswith a set of isolating contacts, wherein said isolating contacts areoperated by the interlock circuit relay.

17. A burner installation according to claim 2 including an interlockcircuit including a relay wherein the contacts of the pressure sensitiveswitch are connected across the supply in series with a relay whichoperates normally open contacts connected in series in the interlockcircuit in parallel with hold on contacts operated by the interlockcircuit relay.

18. A burner installation according to claim 6 having a valve test alarmactuating circuit which includes a relay wherein said relay operatesnormally closed contacts connected in series in any one of circuitscontrolling electrical ignition apparatus, pilot fuel shutoff valves andmain fuel shutoff valves.

19 A burner installation according to claim 1 and including a flowrestricting orifice between said enclosure and said source of suction,and a valve test alarm means, said control means rendering said alarmmeans operative after the elapse of a predetermined time interval timedby said timing device and commencing at the instant of said applicationof said source of suction to said enclosure unless said pressure sensorindicates that said shutoff valves are closed.

20. A burner installation according to claim 1 and including a valvetest alarm means, said control means rendering said alarm meansoperative after the lapse of a predetermined time interval timed by saidtiming device and commencing after the termination of said applicationof said source of suction to said enclosure unless said pressure sensorindicates that said shutoff valves are closed.

21. A burner installation according to claim 14 wherein said controlmeans renders said alarm means operative after the elapse of a furtherpredetermined time interval timed by said timing device and commencingafter the termination of said application of said source of suction tosaid enclosure unless said pressure sensor indicates that said shutoffvalves are closed.

22. A burner installation according to claim 1 wherein said source ofsuction comprises an ejector, a supply of compressed air being connectedto an inlet of said ejector, and a stop valve being connected in a linebetween said ejector and said enclosure.

23. A burner installation according to claim 22 wherein said supply ofcompressed air is that which supplies said burner with combustion air.

24. A burner installation comprising a fuel line, two shutoff valvesconnected in series in said fuel line and defining between them anenclosure, an air line for supplying air for combustion to the burner ofsaid installation, suction means for reducing the pressure in saidenclosure, said means comprising an ejector, an inlet for main flowfluid of said ejector being connected to said air line, means forisolating said enclosure from said ejector, and means for checking thatthe pressure conditions in the enclosure, after said suction means hasreduced the pressure in the enclosure, prove that said shutoff valvesare closed, said checking means comprising a pressure sensor connectableto said enclosure.

25. A burner installation according to claim 3 wherein said means forapplying said source of suction to said enclosure includes a restrictingorifice between said enclosure and said source of suction, said alarmcontacts of said timing device being actuated after a predetermined timeinterval timed by the timing device and commencing upon the applicationof said source of suction to said enclosure.

26. A burner installation according to claim 2 wherein said means forapplying said source of suction to said enclosure comprises a stopvalve, electrical means for operating said stop valve including in itscircuit stop valve contacts of the timing device actuable to open thestop valve for a period, sufficient to allow the source of suction toreduce the pressure in the enclosure to the predetermined reducedpressure, and then to close the stop valve at the start of thepredetermined time interval, the alarm contacts being actuated after apredetermined time interval timed by the timing device and commencingupon the closure of the stop valve.

1. An automatically controlled burner installation comprising a burner,a fuel supply line to said burner, two fuel shutoff valves connected inseries in said line and defining between them an enclosure, means fortesting the effectiveness of closure of said shutoff valves, and meansfor automatically controlling the operation of said burner, said meansincluding a timing device, said timing device enabling said controlmeans to control the operation of said burner in timed order, saidcontrol means causing the actuation of said testing means in a period inwhich the valves are closed, said testing means including a pressuresensor which can be put in fluid communication with said enclosure, anda source of suction applicable to said enclosure, and means forapplying, during a test, said source of suction to said enclosure toreduce the pressure in said enclosure, a check being made after apredetermined time by said pressure sensor that the pressure conditionsin said enclosure prove that said shutoff valves are closed.
 2. A burnerinstallation according to claim 1 wherein the pressure sensor comprisesa pressure sensitive switch actuated when subjected to a predeterminedreduced pressure.
 3. A burner installation according to claim 2 andwhich includes an electrIcally operated valve test alarm, said timingdevice of said control means having alarm contacts operative in an alarmactuating circuit, the pressure sensitive switch also being included inthe alarm actuating circuit the arrangement of which is such that thealarm will be operated upon the actuation of the alarm contacts of thetiming device unless the pressure sensitive switch is in the actuatedcondition.
 4. A burner installation according to claim 3 wherein saidmeans for applying said source of suction to said enclosure comprises arestricting orifice and a stop valve between said enclosure and saidsource of suction and wherein means for operating the stop valve iselectrically operated and the stop valve operating means includes in itscircuit stop valve contacts of the timing device, which are so actuatedthat the stop valve is open for a first predetermined time intervaltimed by the timing device to open the source of suction to theenclosure and shut for a second predetermined time interval timed by thetiming device, the alarm contacts of the timing device being actuated atthe ends of both the first and second predetermined time intervals.
 5. Aburner installation according to claim 3 comprising isolating contactsoperated on actuation of the alarm and included in an interlock circuitof the installation in a manner such as to prohibit, under alarmconditions, the initiation or continuation of a burner control run.
 6. Aburner installation according to claim 3 wherein the alarm actuatingcircuit includes a relay and wherein means are provided for maintainingthe alarm until cancelled by operation of reset means.
 7. A burnerinstallation according to claim 6 and comprising isolating contactsincluded in an interlock circuit of the apparatus in which the relayoperates said isolating contacts in the interlock circuit.
 8. A burnerinstallation according to claim 6 in which the relay operates a pair ofcontacts connected in series in a circuit with the alarm.
 9. A burnerinstallation according to claim 6 and having an interlock circuitwherein the reset means operates isolating contacts included in theinterlock circuit in series and operating in a manner such as toprohibit the initiation or continuation of a burner control run unlessthe reset means is in the inoperative condition.
 10. A burnerinstallation according to claim 3 wherein means are provided forensuring the return of the timing device to its starting positionwhenever the electrically operated alarm is actuated.
 11. A burnerinstallation according to claim 3 in which actuation of the testingmeans takes place prior to the opening of the fuel shutoff valves andalso after the closure of said valves wherein there are providedcircuits alternative to those operative for the testing sequence priorto opening the fuel valves, the timing device having a pair of contactsin each of the circuits and actuable to determine a period during whicheach of the alternative circuits is operative.
 12. A burner installationaccording to claim 11 wherein there is provided in each of thealternative circuits a pair of isolating contacts operable so as toisolate one of the alternative circuits when the other is to beoperative.
 13. A burner installation according to claim 11 and includinga stop valve operated by electrical means including a circuit havingstop valve contacts of the timing device wherein there is connectedacross the contacts of the timing device in the stop valve operatingcircuit a further set of contacts of the timing device operating for thetesting of fuel shutoff valves after the closure of said shutoff valves,said further set of contacts being so actuated that the stop valve isopen for a first predetermined time interval timed by the timing deviceto open the source of suction pressure to the volume and shut for asecond predetermined time interval by the timing device, said alarmcontacts of said timing device being actuated at the ends of both thefirst and secoNd predetermined time intervals.
 14. A burner installationaccording to claim 13 wherein there is provided a set of isolatingcontacts in series with each of the pairs of contacts of the timingdevice, one set of isolating contacts being closed when the other setare open.
 15. A burner installation according to claim 12 and having aninterlock circuit including a relay, and alternative valve test alarmactuating circuits comprising isolating contacts wherein the isolatingcontacts are operated by said interlock circuit relay.
 16. A burnerinstallation according to claim 14 having an interlock circuit includinga relay and a stop valve operated by one of two sets of stop valvecontacts in parallel, each set being connected in series with a set ofisolating contacts, wherein said isolating contacts are operated by theinterlock circuit relay.
 17. A burner installation according to claim 2including an interlock circuit including a relay wherein the contacts ofthe pressure sensitive switch are connected across the supply in serieswith a relay which operates normally open contacts connected in seriesin the interlock circuit in parallel with hold on contacts operated bythe interlock circuit relay.
 18. A burner installation according toclaim 6 having a valve test alarm actuating circuit which includes arelay wherein said relay operates normally closed contacts connected inseries in any one of circuits controlling electrical ignition apparatus,pilot fuel shutoff valves and main fuel shutoff valves. 19 A burnerinstallation according to claim 1 and including a flow restrictingorifice between said enclosure and said source of suction, and a valvetest alarm means, said control means rendering said alarm meansoperative after the elapse of a predetermined time interval timed bysaid timing device and commencing at the instant of said application ofsaid source of suction to said enclosure unless said pressure sensorindicates that said shutoff valves are closed.
 20. A burner installationaccording to claim 1 and including a valve test alarm means, saidcontrol means rendering said alarm means operative after the lapse of apredetermined time interval timed by said timing device and commencingafter the termination of said application of said source of suction tosaid enclosure unless said pressure sensor indicates that said shut-offvalves are closed.
 21. A burner installation according to claim 14wherein said control means renders said alarm means operative after theelapse of a further predetermined time interval timed by said timingdevice and commencing after the termination of said application of saidsource of suction to said enclosure unless said pressure sensorindicates that said shutoff valves are closed.
 22. A burner installationaccording to claim 1 wherein said source of suction comprises anejector, a supply of compressed air being connected to an inlet of saidejector, and a stop valve being connected in a line between said ejectorand said enclosure.
 23. A burner installation according to claim 22wherein said supply of compressed air is that which supplies said burnerwith combustion air.
 24. A burner installation comprising a fuel line,two shutoff valves connected in series in said fuel line and definingbetween them an enclosure, an air line for supplying air for combustionto the burner of said installation, suction means for reducing thepressure in said enclosure, said means comprising an ejector, an inletfor main flow fluid of said ejector being connected to said air line,means for isolating said enclosure from said ejector, and means forchecking that the pressure conditions in the enclosure, after saidsuction means has reduced the pressure in the enclosure, prove that saidshutoff valves are closed, said checking means comprising a pressuresensor connectable to said enclosure.
 25. A burner installationaccording to claim 3 wherein said means for applying said source ofsuction to said enclosure includes a restRicting orifice between saidenclosure and said source of suction, said alarm contacts of said timingdevice being actuated after a predetermined time interval timed by thetiming device and commencing upon the application of said source ofsuction to said enclosure.
 26. A burner installation according to claim2 wherein said means for applying said source of suction to saidenclosure comprises a stop valve, electrical means for operating saidstop valve including in its circuit stop valve contacts of the timingdevice actuable to open the stop valve for a period, sufficient to allowthe source of suction to reduce the pressure in the enclosure to thepredetermined reduced pressure, and then to close the stop valve at thestart of the predetermined time interval, the alarm contacts beingactuated after a predetermined time interval timed by the timing deviceand commencing upon the closure of the stop valve.